The present invention relates to an electric power steering apparatus provided with a torque sensor for detecting steering torque applied on a steering member of a vehicle and a control unit for outputting control signals to drive a motor for steering assist, based on the steering torque detected by the torque sensor.
The electric power steering apparatus equipped on a vehicle supports the steering of the vehicle with a motor, and is composed of a torque sensor for detecting steering torque applied on the steering member and a motor for steering assist that assists the operation of a steering mechanism where the steering member is linked by way of a steering axis. The motor for steering assist is so driven as to obtain power assistance in accordance with the steering torque detected by the torque sensor, thereby reducing the power to operate the steering member. In addition, the power assistance can be changed according to the speed of the vehicle so as not to make the power to operate the steering member too small while the vehicle is being driven at high speed.
In such an electric power steering apparatus, the power assistance is predetermined according to the steering torque and the speed of the vehicle. Therefore, the steering torque necessary for steering differs depending on the reaction forces from the road surface and the vehicle side, which lets a driver know the conditions of the road surface. However, in the case of physically disabled or senior drivers, the wheel might slip through their hands, and there are cases where it is desired to drive at the steering torque determined regardless of the conditions of the road surface.